The high molecular weight (HMW) brominated epoxides (BE) to which the invention refers have the general formula (I)
wherein n is an integer.
They are end-capped by glycidyl groups. This invention is concerned with HMW BEs modified with tribromophenol (TBP). If both of the end glycidyl groups are substituted by tribromophenyl-oxo-2-hydroxypropyl groups, the resulting compounds are phenoxy compounds which have the general formula (II)
wherein n is an integer.
However, it may be that only one of the end groups is substituted, resulting in compounds having the general formula (III)
wherein n is an integer.
Mixtures of compounds of formula (I) and/or (II) and/or (III), wherein at least 80 mol % of the end groups are tribromophenyl-oxo-2-hydroxypropyl groups and at most 20 mol % of the end groups are glycidyl groups, will be called herein “fully modified” or “fully end-capped” (HMW MBEs).
Brominated epoxides, unmodified or partly or fully modified with tribromophenol are known in the art. Japanese Laid-open Patent Publication 1-287132 discloses styrene compositions comprising halogenated compounds having epoxy groups at both ends. Japanese Laid-open Patent Publication 5-117463 discloses styrene compositions comprising halogenated epoxides. Japanese Laid-open Patent Publications 62-4737 and 63-73749 disclose a fire-retardant mixture comprising more than 60% of halogenated epoxy fully modified with TBP. Japanese Laid-open Patent Publication 1-170630 discloses using as fire retardant compound a low molecular weight brominated compound 50% end-capped with TBP. All the above compositions are defective in light resistance, heat stability or other properties. U.S. Pat. No. 5,837,799 proposes as a fire retardant compound a mixture of HMW BE unmodified, modified at one end with tribromophenol, and fully modified (20 to 35 mol % is fully capped with tribromophenol). This mixture however is defective in that it will cause gel formation (by cross-linking) when processed with engineering thermoplastics such as polyamides, thus impairing the processing steps.
Low Molecular Weight (LMW) BEs have low viscosity and therefore it is relatively easy to reduce the volatile content to very low levels by using equipment which is known to those skilled in the art. On the other hand, HMW MBEs are very viscous, even at higher temperatures, and it is therefore very difficult to reduce the volatile content to very low levels. It is therefore advantageous to use LMW BEs with very low volatile content as a starting material for the production of HMW MBEs. Japanese Laid-open Patent Publication 2001-310990 discloses BE which may be fully modified with TBP and discloses a method that requires the use of solvents in the polymerization stage to produce HMW MBEs. The compositions obtained according to its teachings are defective because the flame retardant is prepared in an organic solvent and therefore necessarily contains a significant amount of organic volatiles. These volatiles cause metal corrosion and failure of metallic parts which are near to or in close contact with the flame-retarded engineering thermoplastics.
It is therefore a purpose of this invention to provide flame retardant and flame-retarded compositions, which are free from the defects of the prior art.
It is another purpose to provide flame-retarded engineering thermoplastic compositions which have high impact resistance.
It is a further purpose to provide flame-retarded engineering thermoplastic compositions which have high melt flow index and low melt viscosity and maintain these properties under long residence time at high processing temperatures.
It is a further purpose to provide flame-retarded engineering thermoplastic compositions which minimize corrosion of metallic parts that are near to or in close contact with the thermoplastics.